1. Field of the Invention
The present invention relates to 14,15-substituted lanosterols, to pharmaceutical compositions containing such compounds and to the use of these compounds to inhibit the activity of lanosta-8,24-dien-3.beta.-ol 14.alpha.-methyl-demethylase and suppress the activity 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), two enzymes which are important in cholesterol biosynthesis. The overall effect of these 14,15-substituted lanosterols is to decrease cholesterol formation, thereby resulting in lower serum cholesterol levels in mammals.
2. State of the Art
Elevated concentrations of serum cholesterol have been demonstrated by a number of clinical studies to be a major contributing factor in the development and progression of atherosclerosis, a disease characterized by the formation of cholesterol-containing plaques in the aorta and lesser arteries. The plaques tend to clog the arterial passage ways, making it difficult, if not impossible, for blood to flow from the heart to various tissues in the body. This pathobiological condition can ultimately lead to Coronary Heart Disease (CHD). See, e.g., Kannel et al., Ann. Intern. Med., 90:85-91 (1979); Final Report of the Pooling Project, J. Chron. Dis., 31:201-306 (1978). By maintaining low cholesterol levels in the blood, arterial plaque formation and CHD can potentially be avoided. See, e.g., Brensike et al., Circulation, 69:313-324 (2984) and Levy et al., Circulation, 69:325-337 (1984).
In mammals, serum cholesterol is derived from exogenous dietary sources as well as through endogenous de novo synthesis. Endogenous synthesis of cholesterol involves a complex set of enzyme-catalyzed reactions and regulatory mechanisms which to date are only partially understood. As Rodwell et al., Adv. Lipid Res., 14:1-74 (1976) indicate, 3-hydroxy-3-methylglytaryl coenzyme A reductase (HMGR is generally accepted as the rate-limiting enzyme which controls cholesterol biosynthesis from acetyl-CoA in all organisms. Brown et al., J. Lipid Res., 21:505-517 (1980) have shown that regulation of HMGR is a complex process which is under a feedback control mechanism involving both steroidal as well as nonsteroidal isoprenoid metabolites. The authors point out that under normal conditions, the ability of cholesterol to regulate its own biosynthesis when associated with lipoprotein particles is one aspect of this feedback control mechanism. In addition, it has been demonstrated that various oxygenated sterols, when used in a highly purified state, are even more effective than cholesterol in attenuating the amount of HMGR activity, see Breslow et al., Biochem. Biophys. Acta, 398:10-17 (1975), Kandutsch et al., J. Biol. Chem., 252:409-415 (1977), and Chen et al., J. Biol. Chem., 254:715-720 (1979), leading to the hypothesis that oxysterols may also be endogenous mediators which regulate HMGR activity and cholesterol synthesis in situ. See Kandutsch et al., Science, 201:498-501 (1978).
This proposition stimulated considerable research activity. See, e.g., Chen et al., J. Biol. Chem., 254:715-720 (1979); Havel et al., J. Biol. Chem., 254:9573-9582 (1979); Chang et al., J. Biol. Chem., 255:7787-7795 (1980); Chorvat, U.S. Pat. No. 4,230,626 (1980); Gibbons et al., J. Biol. Chem., 255:395-400, (1980); Kandutsch et al., J. Biol. Chem., 255:10814-10821 (1980); Cavenee et al., J. Biol. Chem., 256:2675-2681 (1981); Tanaka et al., J. Biol Chem., 258:13331-13339 (1983); and Trzaskos et al., Fed. Proc., 44:656, (1985). As a result, a number of inhibitors of HMGR activity have been found.
Gibbons et al., J. Biol. Chem., 255:395-400 (1980), for example, have shown that certain synthetic oxygenated lanosterol derivatives are active inhibitors of HMGR activity. Trzaskos et al., Fed. Proc., 44:656 (1985) have established that in situ generation of the Gibbons compounds leads to attenuated HMGR activity and decreased cholesterol biosynthesis.
In addition, Schroepfer et al., U.S. Pat. No. 4,202,891 and Schroepfer et al., Proc. Natl. Acad. Sci. USA, 81:6861-6865 (1984) have revealed that other oxygenated lanosterol derivatives may be successfully employed to lower serum cholesterol levels in animals.
Additional compounds which affect HMGR and/or other enzymes critical to serum cholesterol biosynthesis are needed. The present invention is directed to this end.